141
FRACTURE ZONE TECTONI CS , CONTINENTAL MARG IN FRAGMENTATION,
AND EMPLACEMENT OF THE KINGS-KAWEAH OPHIOLI TE BELT,
SOUTHWEST SIERRA NEVADA, CALIFO RNI A
Jason Sa leeby
Depa rt ment of Geology and Geophys i cs
University of Ca lifornia
Berke l ey, CA 94720
INTRODUCTION
Sa l eeby (i n press a, in press b). The pa l eogeographic i mplicat ions of the ophio l ite be lt and adjacent metased imentary and metavolcan i c rocks are di s c ussed in Sa leeby and othe rs ( in prep.) . The geochronological evo lu tion of the oph io l ite belt i s
discussed i n Saleeby (in prep. a).
The Sierra Nevada foo thill met amorph i c be lt is
a 450 km long assemblage of remnan t continentderived epiclastics, arc volcanics, pel ag ic-hemipelagic sedi men t s , and ophio l ite s li ces. The various 1 it hol ogic units range in age f rom Ordovician
to Jurassic . Litho l og i c unit s are lenti cular at
sca l es ranging up to 150 km and st rike about N.
30°W. parallel to the trend of the metamorphic belt
(Fi g. 1) . Man y units are penetratively deformed
with a varie t y of near ve rtical foliati on s urfaces .
The 1 ithol ogic units a re generall y bounded by s teep
di pp ing fault and melange zones, but l ocal ly deposi t iona l contacts can be recognized. From at l eas t
latit ude 38°30'N southward, latest Paleozoic t o
possibly early Mesozoic disrupted ophi olite occurs
as remnant oceanic ba semen t beneath Triass ic t o Jurassic arc volcan i cs and interstratified cont inentderi ved epic l astics . Along the northern pa rt o f
thi s s egment o f the metamo rph ic belt the ophiolitic
rocks occur as s cattered basement exposures s urrounded by the younger vo lcanic and epiclastic rocks
(Morgan and Stern, 1977; Behrman, 1978; Saleeby,
unpub. field data). Further south in the KingsKaweah terrane deeper structural level s of the foothi l 1 metamorphic belt a re exposed . Here a nearly
continuous 125 km long ophiol ite belt occurs with
scattered remnants of ea rly Mesozoic ar c vo l can i c
and eplc las t lc rocks depos itionally above It. The
ophi o l ite belt is named i nformall y the Kings-Kawea h
ophiolite belt after the Kings and Kaweah Rivers
which transect it. This ophiolite belt constit utes
part of the same oceanic basement terrane that is
l ocal ly exposed further north amidst the arc vol canics and epiclastics .
Significant conc lusions drawn in this paper are:
1) the Kings-Kawea h ophio l ite be l t or i ginat ed at a
distant ocea ni c sp reading center where cut by a
transvers e fra c ture zone; 2) de fo rmation of the
ophio l ite was progress i ve and occurre d primarily by
fracture zone t ectonics wh il e in route to t he anci en t
continenta l ma rgin; 3) the ancient continenta l margin
was fragmented and tecton i ca lly eroded along an
extension of the fracture zone; 4) the disrupted
ophiolite wa s juxtaposed aga in st the raw edge of the
con ti ne nt as the continental fragments were di sp laced; 5) the di sr upted ophi o l ite was accreted to
the continental marg in as the hanging wall of a subduction zone as a result of a change in p late
motions; 6) the tectonica ll y accreted ophiol ite be lt
subsequen tl y served as frontal arc basement during
s ubduc tion re lated arc activity; and 7) the s uture
between oceanic and cont inenta l basement terranes
rema ined tectonically active as a long itudinal intraarc deforma ti on zone durin g arc activity. Thi s mode l
of ophiolite genes i s , deformation, emp l acement and
s ubsequen t tectonic hi s tory i s be li eve d to be appli cable along the ent ire length of t he Sierra Nevada
foothi ll metamorphic belt (Sal eeby , in prep. b).
The Kings-Kaweah ophiolite belt co ns titutes a
significant segment of the foothill metamorphic
belt. Within it exist the only remnants of a complete ophiol ite succession to be found throughout
the entire Slerran terrane. In addition, since it
represents the deepest exposure of foothi 11 metamorphic rocks, it affords the best opportunity to s tudy
the tectonic and petrogenetic history of the oceanic
basement terrane upon which Mesozoic continental
margin rocks were deposited . The purpose of this
paper is to : l) give a general des c ription of the
ophiolite belt; 2) expand upon cr itical relationships within the ophiolite belt which bear on the
tectoni cs of ophiol ite genesis, deformation and
emplacement , and 3) discuss briefly the tectonics
of the ophlollte belt with respect to the regional
tectonics of the southwest United States. Detailed
structural and petrologic data are presented In
Plate V i s a gene ral geo log i c ma p o f t he KingsKaweah ophiolite be l t. The gross structure of the
belt is that of a huge tectonic megabrecc ia with a
schistose serpentinite matrix. At the north en d of
the be lt clasts range up to 20 km in length, and are
referred to as tectonic s labs (after Hs u, 1968) since
they contain internal mappable st ratigraphic unit s.
The s labs are co ll ective ly named the Kings Rive r
ophiol ite after t he Kings River which transects the
soa b cluster. The slabs are separated by narrow se r pentinite melange zones and by cross - cutting plutons
of the Sierra Nevada batholith. So uthward from the
Kings River area the s labs decrease in size to mono1 ithologlc blocks. In doing so the ophiolite belt
grades into se rpentinite matrix melange . The greater
part of the melange is named the Kaweah serpentlnite
melange after the Kaweah River which transects it.
GENERAL DESCRIPTION OF THE OPHI OLI TE BELT
AND RELATED ROCKS
The Ophi o lite Belt
142
NORTH AMERICAN OPH IOLITES
The ent ire ophiolite belt has been metamo r phosed
in t he a lbi te -ep idot e t o mainly ho rnblende ho rnfe l s
facie s (after Turne r, 1968) by the Cretaceous Sierra
Nevada batho lith. Metamorphic rec ry s tallizati on of
the ophiolite belt is in ma ny places incompl e te .
Thus some insight in to o ri g inal mi nera l ogy of the
ophi o l i te protol i ths is avai I able. In addition, even
_!l~ -·
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where metamor phi c recrystallization i s complete ,
ear lier textures and s tructures are commonly we l !preserved. Thus protoliths of the metamo rphosed
ophi o l ite belt have been rea dily deduced from field,
petrographic, mine ralogical and chemical data .
Detailed treatment o f thi s data is not the intent of
this paper. For sake of brevity the oph iolite wil l
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PLATE 7
KINGS-
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, \OPHIOLITE
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Figure I . Map showing location of King s -Kaweah ophiol ite belt and s ignificant regional geo logical features discussed in text. General geology of Sierra Nevada after Clark (1964, 1976), Jennings and Strand ( 1966), D'Allura
and o thers ( 1977) , Schweickert and others (1977), Sa leeby and others (in prep.) . Paleozoic regional thrust
faults after Burchfiel and Davis ( 1972), Speed (1977) . Paleozoi c pa l eographic belt s after Chu r kin (1974),
Stevens (1977). Pa l eozoic foreland basin axes after Poo l e a nd others ( 1977), Speed (1977), Stevesn (1977).
Early Mesozoic deformation belt after Stewart and others (1966), Burchfi e l and others (1970), Stevens and Ol son
( 1972) , Ke ll ey and Steven s (1975). Initial strontium contours for autocthonous post-Pa l eozoic igneous rocks
after Kistler and Pet erman (1973). Majo r faults and ophiolite fragments of Klamath Mountains and Coast Ranges
after Jennings and Strand (1966). Inset at lower right shows plots of several geological parameters taken along
a section perpendicular to southern part of foothill s uture. Bouquer gravity after 01 Iver and Robbins (1975) ;
rock density after Cady (1975), Saleeby ( 1975) ; heat f l ow after Lachenbruch (1968); isotopic composition on
autocthonous igneous rocks after Kistler and Peterman ( 1973), Dow and Oelevaux ( 1973), Sa l eeby (1975), Chen
(1977); composition of volumetrically Important Mesozoic plutons after Mcore (1959), Saleeby (1975), Chen (1977)
with gb•gabbro, qd~quartz diorite, gd 0 granordiorl~e, q11Fquartz monorite.
KINGS-KAWEAH OPHIOLITE BELT - SALEEBY
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Kings - Kaweah ophiol i te be lt . For compa ri son l eft
co l umn shows normal oceani c basement af ter Ludwig
and othe r s ( 1970) , Sutton and othe r s ( 1971), Chri st ensen and Salisbury (1975), Clague and St raley (1977).
otrOA:HlD
be di scussed in terms of pre-batho l ith proto l iths.
For furt her information on batholith re l ated me tamorphism see Saleeby (1975, 1977 , in press a and b,
in prep. a).
The Kings River ophi o l i t i c s l a bs are named afte r
t he highest encompassed peak. The s l abs are bounded
by se rpe nt in ite me lange zones i n most instances.
Where no t pr esent, the me l ange zones can be inferred
to have existed pri o r to batholith emplacement. The
Hog and Ti vy Mo untai n slabs are predominantly per idotite . Th ese s labs grade into the nei ghbo ring
me l ange mat ri x. Peridot ite fo liati ons gra de i nto or
are cut by domains of sch i s tose se rpen t inite.
Towa rds the melange zones the schi s t ose serpentinite
domains become dominant until the o ri g inal peridotite fabric a nd mineralogy i s obliterated producing
th e me lange matrix . Within s ho rt distances exot i c
blocks of gabb ro, basalt and chert occu r wit hi n the
serpentinite mat ri x. The st ri ke of t he matr i x schlstosi t y is parallel to the long axes of the s labs a nd
to the reg iona l trend of the ophi o lit e belt.
Within the s l abs s truct ures whi ch pre-date
melange mix ing also occur. Per i dotite and gabbro
within the Hog Mounta in and Tivy Mountai n s l abs conta in a my lonitic foliation. The trend of thi s fo li ation is main l y parallel to the trend of the oph iolite belt. However, doma ins in which fo liati ons have
been fo lded and rotated are common. The fo l ded and
rotat ed domains are truncated by my lonite fo li at ion
s urfaces which are identical to the folded s urfaces .
Structural analys i s of the mylonites shows that myloni tization proceeded in repeated pulses with ea rlys tage fo l iation s urfaces being truncat ed, rotated,
fo l ded and refo lded during succeeding stages of myloni tization . Thi s complex family of foliation s urfa ces i s referred to as SJ. Within SJ there Is a
steep plunging lineat ion (L1) defined by elongated
dimensional ma rker s s uch as pyroxene porphyroclasts
and deformed mafic inclusions. Folding of S1 and L1
was predominately abo ut s teep plunging axes . Folds
in s 1 and Li are referred to as FJ. Fi geometry is
variable and comp l ex. Asymmetries suggestive of a
dextral sense of motion are not uncommon.
The s chistos i ty of the me l ange ma trix and s imilar sch i stositics of the Hog Mountain and Ti vy Mountain s labs are r eferred to co ll ect i ve ly as s2 . Along
bot h margins of the Hog Mounta in slab , and al ong the
weste rn margin of the Tivy Mountain s l ab SJ g rades
in to S2. This i s manifested by a progressive in crease
of schis tose serpent ine relati ve to flattened and
st rea ked o ut oliv ine and pyroxene. Along t he easte rn
marg i n of the Tivy Mo untain s l ab S2 cuts sharp ly
across SJ. Loca l zones of both S2 c utting S1 and S1
grading into s2 occur wi thin the u l tramafic s labs .
S1 in northwest orienta ti ons grades into s 2 , whereas
SJ in other or i enta tions i s cut by 52.
Maf i c s labs of Ba l d Mountain and Hu ghes Mounta in
conta i n a re li ct s hear fab ri c which i s on l y loca ll y
deve l oped i n each of th em except fo r the northwe st
part of the Hughes Mo untai n s lab where it i s penet rative . The s hea r f abric i s a l so steep ly dip p ing and
pa ra! l e i t o the regiona l trend of the op hi o lite be lt.
It i s thought to be equ i va l ent prima ril y to S1 of t he
Hog Mountain and Tivy Mountain s l abs. Simi l a r shear
fab ri cs in mafic me l ange blocks appear to be s urfaces
al ong whi ch the bl ocks were r ifted apart during
me l ange m1x1ng. Th us the s hea r fabric may i n part
also be equival ent to S2 of t he ult ramafic s labs and
me l ange zones. As will be disc ussed l ater, deve lopmen t of s 1 and s2 a re t ho ught to have part l y overlapped in time.
The s labs conta in va ri o us segments of the o ri ginal ophi o li te s tratigraphy. A r econst ructed st rat i graphic secti on i s s hown in Figure 2. Next to the
graphic sect ion the interva l s s panned by the Kings
River s labs a re s hown. The reconstructed st rata !
thicknesses are taken from the Tivy Mo un tai n and the
Bald Mountain s labs wh i ch fit imme di ate ly adjace nt to
one another when the ophi o l ite i s pal inspastica lly
resto red to its pre-batho l ith configuration (Fig. 3).
The reconstructued o phi o lite section cons ist s from
the base up of : 1) greater tha n 4 km harzburgi tedun i te with traces of chromitite, wehrlite, c linopy roxenite and gabbro; 2) 2. 5 km mafic- ultramafic
transi tion zone composed of the same rocks except
wehrlite, c li nopyroxenite and gabbro are more
144
NORTH AMER ICAN O PHI OLITES
significant; 3) 2 km gabbro and lesser cl inpyroxenite cumulates; 4) 0.7 km basalt-diabase dike comp l ex
which i s loca ll y sheeted; 5) 1.8 km ba saltic p illow
lava and pi I low breccia; and 6) greater than 20 m
metalliferous radiolarian chert. The reconstructed
oph i ol ite section is interpreted as a sample of
oceanic crust and upper mant le . A more detailed
di scus sion of the ophiol i te section is presented in
Saleeby (in press a).
Southward from the Kings River area the oph io 1 i te fragments decrease in size to form tectonic
blocks in serpenti n ite me l ange. Th e large gabbro
block at the north en d of Smith Mount~in i s Int ermed ia te i n size between the Kings River s labs and
common melange blocks which range between I km and
seve ral meters in diameter. Geophysical data
(Saleeby, 1975) indicates that the Smith Mountain
block continues in the subs urfa ce for at least 7 km
no rt h of Smith Mountain. A significant feature of
the serpentinite melange is that it consists only of
ophio lite assemb lage blocks. Blocks of dun ite, harzburgite, wehrl ite, cl inopyroxenite, gabbro, ma fi c
dike rock, pillow basa lt,ophi calcite and radiolarian
chert are s uspended in schistose serpentinite.
Ultramafic blocks usually grade o utward into the
mat ri x in a fashion s imilar to that desc ribed for the
ultramafic s lab s of the Kings Rive r area. In contras t, contacts between matrix and ma fi c and chert
me l ange b locks are usually sharp .
Me lange blocks are invariabl y e longate parallel
t o the matrix schistosi t y and the regiona l trend of
the oph io l ite be l t. Inte rna l s truct ures of the
blocks such as mylonite o r metamorphic foliation a nd
shear surfaces are usua ll y or iented parallel to the
blocks long axes . Ch e rt blocks are usuall y tab ular
in shape with bedd ing a l so o ri ented para l le l to long
axes. Many me lange blocks have transverse extens ion
fractures which are occasionally injected with schlstose serpentinite. In many instances b locks have
been pulled apa rt along the tension fractures l ike
l arge boudins . Local kinks in blocks and sma llscale fo l ds in the matri x schistosity occur; these
are invar iably about near vertical axes with many
of them having as ymmetries indicating a dextral sense
o f mo t ion.
Outc rop mapp ing of the me lange revea l ed a clustering of blocks of simi lar 1 it ho logy or litho logi es.
The c lus ters are shown as melange units on Plate 1.
The melange uni t s appear to be the vestiges of once
larger bl ocks or s labs that have been d istended into
a myr iad of sma ller blocks by fau lti ng and injection
of the more mobi le matrix. Within the me l ange units
there a re vestiges of primary igneo us and sed imentary
contacts between di fferen t members of the ophio lite
assemblage. As discussed below, some primary contacts fo rmed during me lange developmen t. The me lange
un its are interpreted as the mixed remnants of ocean
floor s trati graph 'c success ion s . Stratigraphic
s uccess ions reconstructed from the unit s are a l so
shown in Figure 2. The imp lications o f the reconst ructions wi l l be d i scussed below .
Continenta l Margin Rocks
Depos itiona l remnants of continenta l margin
roc ks occur above t he Kaweah serpentinite me l ange.
The oldest of these rocks is a chert-argilllte olistostrome complex containing ol istollths of sha l low
water limestone and interbeds of chert and quartzose
to subarkoslc sandstone. The shallow water l imes tone
blocks contain late Permian fauna bel leved to be ,
exotic to North Ame rica (Saleeby and others, in
prep). The chert-argillite comp l ex grades i nto a
volcanic arc-ep icla st i c sequencL Che rt deposition
apparently subs ided or was overwhelmed as quartzose
to s ub-arkosic flysch deposition and basalt-andesite
volcanism commenced. The continenta l margin rocks
were faul ted, folded and f latt ened along with latestage defo rmati on of it s oph io l itic basement. Depos ition of this assemblage appears to have been syntectonic with abunda nt intraformational rework i ng.
In addition, local uplifts a nd expos ures of ophi ol ite basement shed oph io lite assemblage o l istostromes
into the continental margin rocks. Age constraints
on the depos iti on of conti nental margi n rocks pl ace
it between the latest Permian and late J urassic
(Sa leeby and others, in prep.).
Midd l e and la te Ju rassic gabbroic to quartz
dioritic pluton i c rocks wh ich cut the ophiolite be l t
appear to be the roots of the volcanic arc rocks
(Sa l eeby, 1975; Sa l eeby a nd Sharp, 1977). An important feat ure of the p lu tonic rocks is that they were
emp l aced l a t e in t he de formation history of the
oph iolite be lt fo ll owing significant t ectonic mixing.
Thus the plutons cut melange st r uct ures and are
struc t ura ll y in tact, but have high temperature deformation feat ures on trend with the s truct ure of the
ophiolite belt. The structural re lation between the
ophiol ite be l t and the Jurassic plutons is analogous
to the structura l re l ation between the depos i tional
remnants o f continental margin rocks and the ophio1 i te be l t. The petrogenesis of ea ch was late-sta ge
syntectonic a long the pre-ex isting s tructu ra l t rends
of the ophio l ite basement. Fo liat ion surfaces of the
Ju ra ssic plutons and the continental marg i n rocks are
designated s on Plate V.
3
The ophiolite be l t is in tectonic contact along
its eastern margin with an additional assemb la ge of
continental ma rg in rocks. Thi s assemblage consists
of quartzite-argi I li te o l istostromes , qua rtzose to
sub-a r kosic massive sandstone and flysch, carbonate
turbi dites and slide blocks and an upper section of
shallow marine and si l iclc volcanic rocks. It is
thought to be equivalent to the upper intervals of
the Ca l a ve ra s Complex exposed further north al ong
the foothi 11 me tamorphic be l t (Sa l eeby and Goodin,
1977; Schweickert and ot hers, 1977). Late Triassic
t o early J urassi c fossils have been recovered from
the upper pa rt of this assembl age (Christensen,
1963; Jones and Moore, 1973; Sa leeby and others, in
prep.). Recent mapp i ng and petrog raph ic work suggests that part of this a ssemb lage is a proximal
facies of the epiclastic rocks deposited on top of
the ophio l ite (Sa leeby and othe r s, in prep.).
Geochrono logy
Geochronological work in conj unct ion with structu ral and petrologic work has revealed a pro longed
history of igneous and metamorphic events along the
ophiolite be lt . Gabbro of the Kings Ri ve r ophi o l ite
transi tion zone contains rare pods and d ike lets of
diorite and plagiogranlte whi ch appear to be au tocthono us magmatic differen tia tes. Zircon sepa rates
from the se rocks and s iml Jar rocks from three widely
spaced gabbro-peridotlte blocks from the Kaweah serpenti nite me lange yield a s uite of di sco rda nt U/ Pb
ages whose minimum ages range between 205 m.y . and
270 m.y ~ an d whose upper Intercep t age s cluster around
300 m.y. Zircon discordance is attributed to Cretaceous therma l metamorphism re l ated to emplacement of
the batho l ith. Intercept age s on young zircon populations are difficult t o interpret . The tentative
145
KINGS-KAWEAH OPH IO LIT E BE LT - SALEEBY
inte r pre t at ion i s that i ni t ia l crys ta ll izat ion cou ld
have ra nged back t o 300 m. y. ; however, it could have
occurred as l a t e as about 250 m.y. Si nce the sparce
l eucocratic rocks are an i ntegral part of the oph io1 i te belt's igneous assemb lage, the i r i nitia l crysta l ! i zat ion age const r a i nts are taken as oph io l ite genes i s age constra i nts.
Reg iona l the rma l metamo r phi sm re la t ed to the
Si e rra Ne vada ba tho l i th i s of ho r nb l ende horn fels
f ac ies . A s i gni f i can t except ion i s whe re loca l zones
o f al b i te-ep i dote ho r n fe l s facies roc ks occur at
s i gni f i can t d i stances f rom contacts wi th batho l i t h ic
rocks . From these zones maf i c metamorph i c tecton ites
of the oph io l i te have been dated by K/A r techn iques.
The mi n imum age o f these tecton i tes is 190 m. y.
Where s imil ar tecton i tes have been co ll ected from
zones of hornb lende hornfe l s fac i es rocks the K/Ar
sys t em has been comp l ete l y r eset to batholith ages.
As d i scussed be l ow , mesoscopic f i e l d relat ions suggest t ha t the tr ue metamorphic age of these tectoni t es i s the same as the oph i o l ite genesis age .
TIVY
MTN
SLAB
VENICE !-/ILLS AREd__
KA WEAH RIVER AREA_
The timing of oph io l i te de format ion is bounde d
on the uppe r end by vo l um i nous p l utons of the batho l i t h whi ch cut S1, s1 and s and l ack a tecton i c
f abr i c. These plutons have y3 ie lded numerous ea rl y
Cre t aceo us concordant z ircon ages . The intac t p l uton i c rocks whi ch conta in S3 but cu t me l ange st ruct ures have yie lded concorda nt mi dd l e and late J urass i c z i rcon ages. Th us tecton i c mi x ing of the oph io1 ite be lt ceased by midd l e Ju rass i c ti me and subseque nt defo rmation of the ophio l ite belt and Jurass i c
p l utons ceased by ear ly Cretaceous time. The tectoni cs of ophio l i t e genesis, transpo r t, defo rmation ,
me l ange deve lopment and emp lacement a r e the subjects
of the r ema i nde r o f t hi s paper.
EXPLANATION
DEPO S ITIONAL REMN ANTS OF
CHERT
PILLOW LAVA MOUND
CHERT BLOCKS
D
Fi gure 3 . Pa l i nspas ti c r esto r ation of the
Kings-Kawea h ophi o l i te be l t to i ts conf i gura·
t ion pr io r to emp l acement of Ju rassic a nd
~ retaceous p l utons of t he Si e r ra Nevada
bat ho lit h , ove rl ap by cont i nenta l margin
rocks , and t ecton i c j uxtapos i tion i ng
aga i nst t he Ca lave ras Complex.
OPHICALCITE, DETRITAL
ITE AND MAF IC CLASTI C
PILLOW LAVA, BRECC IA AND MAFI C DIKE
ROCK
GABBRO AND PYROXENITE
IOKm
MAF IC TECTONITE LE NSES
BLOCKY FRACTURED SERPENT INI ZED DUNITE ,
HARZBURGITE AND LESSER WEHRLITE
TECTONITIC DUN ITE, HARZBURG IT E AND LE SSER
WEHRL ITE
D
SCHI STOSE SERPENTIN ITE
-- ._I_ULE RIVER
AREA
146
NORTH AMER ICAN OPHIO LITES
c
TH E FRACTURE ZONE MODEL
A palin s pa s ti c resto rat ion of the ophi o l i te
be l t to it s conf i gura tion pr io r to emp lacement of
Jurass i c to Cretaceous p lu tons and deposition of the
con t ine nta l ma rgin asse mbl age i s s hown in Fi gure 3.
The r econs truct ion s hows the ophi o l i te be l t as a
tec tonic megabrecc i a with a penet rative verti ca l
p la na r fabr i c. Thi s conf i gurat io n i s s i gn i ficant l y
d i ffe re nt f rom ma ny other oph io l ites wh i ch occ ur as
moderate l y dipp ing sheets (Moores, 1969; Co l eman , 1971;
Davi es , 1971; Dewey a 11d Bi r d, 197 1; Moores and Vine,
1971 ; Chur ch, 1972; Gea ley , 1977). For thi s reason an obduct ion o r ove r thrus t mode l of emp l aceme n t
i s not adopted fo r the Kings-Kaweah oph io l ite be l t.
A contine nta l marg i n s ubduc t ion mode l of e mp l aceme n t does not s eem applicab l e e i ther. The tecton ic
me l ange of the King s-Kaweah oph io l ite be l t i s ocea ni c
in o r1 g 1n . Con tine n ta l ma r g i n rocks were de pos i ted
across oph io l ite me l a nge l ate in i t s deforma tiona l
h i sto ry s ubseque nt to s i gnifi can t te c t oni c mixing.
In ad diti on, t he sedimentary r ecord o f the ophi o l ite
be l t reco rd s tra nsport from the oceanic regime i n t o
a continen t a l marg i n reg i me wh i ch was c haracte ri zed
by non-vo l can i c hemi-pe l ag i c and te rr igenous sedi me ntatio n. A vo l can i c arc was not a pproached by the
sea f loor spreading trans port of the ophio l ite a s
wou l d be t he case i n a s ubduct ion emp l acement mode l.
Fi na ll y, metamorphi c t ectonites o f t he ophi o l ite
be l t are g reenschi s t to amphibo l ite fac ies . Blueschi s t and ec log i te fac ies rocks, which are general ly
cons ide red characteri s ti c of s ubduc ti on compl exes,
are not present along the Kings - Kawea h be l t.
An alternat i ve to an o bduct ion o r s ubduc ti on
mode l of ophi o l ite deforma ti on and emp l acement i s
deve loped be low. Specif i c s truc tu ra l , pe tro l og i c
and s t ratigraphi c r e l ations a long t he oph io l i te be lt
are use d in conj uncti on wi t h recent d i s cove ri es in
marine tectoni cs t o deve lop an oceanic f rac ture zone
mode l . The ro l e of some of the re l a ti ons hips used
t o deve lop the mode l i s s umma r ized in Fi gure 5.
Re l ations hi ps between pe trogenes i s and de fo rmat i on
o f t he ophi o l ite a re of pr imary Interest . Cri t i ca l
re l ations h i ps in i gneous , pre-bat hol ith metamo rphi c,
and ocean i c sedi mentary rocks a re covered res pec tive l y . Emphasi s i s pl aced on the fact that defo rmati on and d i s r uption of the ophi o l ite was oceani c
and p rog ress ive, and f urthe rmo re, oph io l ite genes i s
was syntecton i c . Spec i f i c re lati ons hips di scussed
be low may ha ve notewo r thy a l te rnat i ve in terp retations . Howeve r , i n each i nsta nce t he fr act ure zone
inte rpretati o n a ppea r s to be as good o r bette r than
a l ternative inte rp re tat io ns . Furthe rmo re , when a ll
of the relation s hips a r e cons idered t ogethe r, the
fra c tu re zone mode l seems to be t he onl y mode l that
cannot be dism i ssed. For sa ke o f brev ity the a l ternative inte r pr e tat ions will not be g ive n eq ua l treatmen t.
Igneous De forma tion
Tempo ral re l ations h i ps betwee n the i gneous generat ion of the ophl o l ite be l t a nd commencement of It s
deformat ion history s uppo rt the fract ure zon e mode l .
Deve l opment of Sj commenced during the i gneous gene ration of the oph o l ite at t he ocean i c sp reading
KINGS-KAWEAH OPHIOLITE BELT - SALEEBY
147
Figure 4 . Photographs o f some i mporta nt features a long the Kings -Kaweah ophio l ite be l t. A: Protoc l asLic defo rma t ion in diorite and basa l t d i kes cutting cl i nopyroxene ga bbro. B: Deformed hydrothermal veins i n harzburgite
tectonite; ve in s are f l attened into S1 wh i ch i s tight l y folded around vert i cal axis with homoaxial open refo ld.
C: Bl ocky fracturing i n se rpentinized harzburgite. D: Large c last of oph i ca l c ite composed of sma ll er ophicalcite c l asts (areas ri ch in dark u l tramafic detritus ) in mi crit i c matrix; the l arge clast occurs with other
c l asts of peridotite and oph i calcite within a micritic mat ri x. E: Crude bedding in sedimentary serpentin lte;
up pe r bed contains up to bou l de r s i ze c l asts, lower bed conta i ns up to cobble s ize clasts. F: Steep-p lunging
~ l o n gat i o n l ineat ion in harzburgite; L
i s accentuated by transposed hydrothermal veins. G: Soft sed iment
1 radiol ar ian chert; dark bands are nearly pure ox ide mineralsi note
fo l d i ng and brecc i ation in meta ll iferous
how disrupted i nterval i s bounded by intact interva l s.
center . Intrusive and extrusive pu l s es over l apped
in time wi th pul ses of my lon i t i zat ion. Some in tr us i ve masses c ut S1 sharply a long part of t heir l e ngth
but are in turn c ut o r transposed i nto S1 fur t her
a long t he ir l engt h. Some me re l y s how chaot i c protoc l ast i c -type st ructures wh ich in most cases converge
into s 1 of the su rrounding rocks ( Fig . 4a).
The positi on and amount of highly diffe rentiated
i gneous rocks ra i ses an i mportant point. Pi I low
lava s o f the ophiol ite be l t are basaltic. Ke ratophyre and quartz keratophyre are apparent ly absent.
The maf ic dike and c umu l ate gabbro zones of the Kings
Ri ver ophi o li te and equ i valent me l ange bl ocks lack
diorite and pl agiogran ite. Thi s paucity of highly
diffe ren tiated rocks contra s ts wi th many othe r oph io1 ites which contain s ignificant amount s of intermediate t o s il icic i nt rus i ve and extrusive rocks
( Moo res, 1969; Dewey and Bird, 1971; Bai l ey and
Blake , 1974; Co l eman and Peterman , 1975). Diorite
and p l agiog r an ite do occ ur i n trace amounts i n the
Kings Rive r transit ion zone and in equ i va lent me lange
blocks. I t thus appea r s that th e on 1y e nv i ro nme nt
s uitab l e for stagnat ion and extreme d i fferent iat ion
of magma bodies was in the deeper l eve l s of the oph i o l i te be neath the main plutonic pa rt of the sect ion .
The pockets and dikes of magma wh ich s tagnated in
t he transition zone a l so concentrated magmatic water
during differentiation . This is shown by the presence of pri mary brown hornblende and by hy.drotherma l
aureoles and veins that formed in t he ultramafic host
rock . In t he hyd rot he rma I zone s dun i te, harzb u rg i te
and wehrllt e have been a ltered to var i ous combinations of serpentine, Cr-chlor ite and ta l c (F i g. 4b) .
An important feature of Lhes e a l teration zones is
that they also show developmental pu l ses which ove r l apped in time with my lonitization pu l ses in that
the zones c ut and are cut or transposed by s 1 to various deg rees .
Structural analysis of the s 1 tectonites reveals hi gh amounts of flattening and constr i ct iona l
s train. In addition, persistent pulses of trans lational movements with folding and rotation about
steep axes accompan i ed the flattening and constr i ctional stra in. I t is difficult to envision such complex tectonites forming at a norma l oceanic sp reading center . However, tectonites s imil ar to Lhose
o f the Kings -Kaweah ophi o l ite be lt have been recovered from transve r se fracture zones (Aumento and
ot hers, 1971; Bonatti and ot hers, 197 1; Me l son and
others, 1972; Thompson and Melson, 1972; Bonatti and
Honnorez , 1976; Fox and others, 1976). It is proposed that the s 1 tecton i tes of the Kings-Kaweah
oph iol i te be l t deve loped along a transverse fra ctu re
zone . The s deformation began at the intersec ti on
1
of t he fra cture zone with the ridge ax i s and continued for some unknown distance off the ridge axis .
Thus , p lu ton i c masses and their cont act metamo rphic
der i vatives were protoclastical ly deformed by s 1 and
subsequently fo lded, rotated and redeformed with
development of late r -stage s 1 . It i s important to
emphasize that the penetrative tectonite fa bri c that
i s present throughout the harzb urgite i s al so present in dunite, wehr l ite, pyroxe nite, gabb ro , diabase, dlor i te and plagiogranite. A di st inctive t ecto11 ite-cumu l ate contact or contact zone, as wou l d be
expected with a normal ridge derived ophio lite, does
148
NORTH AMERICAN OPHIOLITES
not exist in the Kings-Kaweah ophiolite belt.
heat are considered the s ame.
Development of s 1 varies with stratigraphic
depth in the reconstructed Kings River opriol ite
section (Fig. 2) . This variation reflects a chan ge
in ma terial behavior with depth during Si development. The harzburgite and l ower transition zones
behaved by penetrative ductile and catac lastic f low .
Notable exceptions to thi s are smal 1 isolated mafic
bodies in the harzburgite zone which syntecton ica ll y
recrystal 1 ized in the amphibo l i te facie s and, intrusive masses in the transition and lower gabbro zones
which were protoclastically deformed. The upper
transition and l owermost gabbro zones behaved similar to rocks lower in the section except in a l ess
penetrative fashion. Thus l ocal domains in which
i gneous textures and structures are fairly-wet I preserved occur within these s tectonite s. The tecto1 part of the gabbro zon e
nites extend through the main
as ductile fault zones. In the mafic dike and p ill ow
basalt zones l oca li zed shear and brittle fracture
zones occur.
Within the deeper stratal l eve l s of the Tivy
Mountain slab gabbroic masses were syntectonical l y
recrystallized to amphibol ites during developme nt of
s 1. Unfortunately, contact metamorphism by the
bathol ith makes it impossible to resolve the original metamorphic grade of the Tivy Mountain slab 's
upper l evels. The same problem exists with the
Bald Mountain and Hughes Mountain s labs which con tain the ophio l i te' s uppermost strata I levels .
What can be said is that metamorph i c recrystallization was nowhere near as perva s ive in the uppe r
level s of the Tivy Mountain slab as in its lower
l evels, and that ductile, cataclastic and protoc la stic flow greatly predominated as deformation
modes in its upper levels. Where the protoliths of
amphibol i te tectonite blocks in serpentinite me l ange
can be deduced, they are usually gabbro . In contrast, low grade amphibo l ite and greensch i st tectonite blocks are most common ly de rivatives of mafic
hypabyssal and volcanic rock .
The general deformation pattern displayed in
the reconstructed Kings River ophiolite section is
increasing ductility and pervasiveness with strata l
depth. This pattern is believed to be primari ly a
result of a steep ocean ridge thermal gradient with
higher temperatures favoring greater duct ii ity and
pervasiveness of deformation. Thi s deformation pattern is beli eved to have been masked by intense protoclasis at the intersection of the fracture zone
axis with the spreading axis . Mafic melange units
commonly contain blocks with extremely complex internal structures in which chaotic mixtures of pillow
lava, mafic dike rock, gabb ro and mafic metamorphic
tectonites have contradicto ry relationships with s 1 .
The chaotic mafic melange blocks are interpreted as
remnants of the intersection zone. The spatial
relationships envisioned between the me lange units
which contain the chaotic mafic blocks and the large
slabs which fit into a mo re conventional oph iol ite
stratigraphy will be discussed below.
The re l ationships out lined above are interpreted as a result of a s teep ocean ridge thermal gradient which controlled metamorphic mineral assemblages developed a long the fractur e zone where metamorphic recrystallization was the prefe rred mode of
deformation . Pervasive amphibolite facie s metamorphism is present between strata l depths of 7 and II
km in the reconstructed Kings River section . With
a temperature range of about 450°C to 6S0°C for the
amphibolite facies (Turner, 1968), this depthtemperatu r e relation corresponds with calcu l ated
ocean ridge geotherms (Oxburgh and Turcotte, 1968 ;
Sclater and Franchetean, 1970). The lower grade
conditions which existed hi ghe r in the section are
manifested by l oca lized zones of syntectonic metamorphic recrys tallization now preserved only within
mafic melange blocks. Thi s localization of metamorphic tectonites at higher strata l leve l s is
thought to be a result of three variables which
worked together to produce them: I) zones of concentrated deformation; 2) a rapidly declining high
thermal gradient; and 3) migration of water . As
discussed below, the zones of concentrated deformation are thoug ht to have widened with time, and as
a result the influx of water into the deforming
ocean floor increased with time . However, the
rapidly declining thermal gradient put tight timespace constraints on the interva l over which metamorphic recrystallization could operate as a significant deformation mode at upper crustal levels.
Metamorphic Tectonites
Recent s tudies of ocean ic ridges and fracture
zones have shown that these zones are c haracterized
by a distinctive steep vertical metamorphic gradient
which passes through zeal ite, greenschist and amphibol ite facies (Miyashi ro and others, 1971; Miyashiro,
1972 ; Spooner and Fyfe, 1973; Fox and others, 1976) .
This vertically compressed facies series apparently
results from a steep ocean ridge thermal gradient
which is related to heat liberated during ocean
floor genesis. The effects of a steep ocean ridge
thermal gradient are evident In the metamorphic
grade of mafic tectonites present along the ophio1 lte belt (Fig. 2). Data which pertain to this
subject comes from within the Tivy Mountain slab and
from zones along the serpentinite melange where contact metamorphism by the batholith is at its lowest
grade. As stated earlier K/Ar data on the maflc
metamorphic tectonites reveals a minimum metamorphic
age of 190 m.y. Contact metamorphism by the batho1 i th has seve rely altered both U/Pb and K/Ar systems
of the ophiolite belt, so the true metamorphic age
of the tectonites ls probably significantly ' greater.
Since protoclastic deformation of dlorite-plagiogranite dikes and metamorphic recrystallization of
the maflc tectonites ·are both s 1 features, the true
metamorphic age of the tectonites is probably close
to the Igneous age of the dlorite~plagiogranite
dikes. Thus metamorphic heat and ophlolite genesis
Progressive se rpentinizatlon of the ophio lite
belt's ultramafic rocks is thought to have been an
important fracture zone process. Serpentinization
is known to be an important process along modern
oceanic fracture zones (Bonatti and others, 1971;
Melson and Thompson, 1971; Bonatti, 1976; Bonatti
and Honnarez, 1976) . Serpentinization of the KingsKaweah belt began with transition zone hydrothermal
metamorphism during ophiolite genesis and initial
deformation. As stated earlier the hydrothermal
zones cut and are cut by or transposed into St to
various degrees. The hydrothermal serpentinites
do not appear to be directly related to s 2-bearing
schistose serpentinltes. However, s2 serpentinization is also thought to have overlapped in time with
development of s 1 . This is suggested by the gradltlonal relations between S and s . s represents
1of the newly
2
the initial deformation anl disruption
created ocean floor. As stated earlier s develop1
ment was progressive. As s 1 developed migration
of
KINGS-KAWEAH OPHIOLITE BELT - SALEEBY
149
ocean water into the deforming ocean floors deeper
stratal l evels was faci 1 i tated. As water migrated
into the ultramafic rocks sy ntecto ni c serpentine
growth progressive l y replaced ductile and catac l astic flow of olivine and pyroxene. Slabs and blocks
of s 1-bearlng peridotites are the incompletely digested remnants of the young ocean f loor's ultramafic
zones. It is important to note that steep plunging
folds which are so common in the Si-bearing s labs
also occur locally in
of the ultramafic s labs and
the melange matrix.
Ultramafic detrital rocks also occu r a long the
oph iol ite belt. These consist of detrital serpentinites and ophica l cltes . Nearly identical rocks have
been recovered from modern fracture zones (Bonatti
and others, 1973, 1974). Rarely fine detri tal serpentini te wi ll occur as sedimentary mat rix for mafic
c la st breccias, and occasiona ll y basa lt and gabbro
clasts occur in oph i ca l cite. The ultrmafic breccias
have complex developmental hi s tories which are directly rel ated to deeper leve l tectonics and a l so Involve abundant surf i cial reworking.
Progressive serpent ini za ti on is believed to
have l ed to greater mobil ity in the young ocean
floor. As s2 domains developed differential tectonic movements were preferentially concentrated
along them. Thi s accelerated both tectonic mixing
and further se rpentinization which led to serpentinite me lange formation. As will be discussed below
protrusions and surficial debris flows of ultramafic
rock appear to have played an integral part in this
stage of the ophiolites disruption history.
A significant number of ultramafic melange blocks
have structural features which differ significant l y
from the s 1-s 2 re l ationships discussed earlier.
Superimposed over the peridoti te foliation (S1) i s a
rounded blocky f racture system with arcuate schi s tose
serpentinite zones woven through the peridotite autoclasts (Fig . 4c) . These featur es grade into several
different features. In some instances the schistose
serpentinite zones become more pervasive, less accurate and ultimately converge into S2 of the melange
matrix leaving sma ll clasts of serpent inized per idotite dispersed in matrix adjacent to the parent bl ock.
In other instances, the serpentinite becomes less or
non- schistose with the clasts di s persed through it in
a chaotic fashion. In a significant number of
instances the ultramafic me lange blocks go th rough
s imilar gradations as mentioned immed iately above
except ca lcite and dolomite occur in different
amounts through the sequence. First the carbonate
occ urs interstitial to ultramafic fragments and then
it progressive ly increases in concentration unti I the
ultramafic material is dispersed in a carbonate
matrix (Fig. 4d) .
Si
Syntectonic Petrogenesis
Structural analysis of the ophlol ite belt's
igneous and pre-bathol ith metamorphic rocks indicates a s yntectonic petrogenesis of the ophiolite
belt's crustal segments which can be best explained
with a fracture zone model. Progress ive deformation
a long the fract ure zone during transport away from
the spreading axis led to the formation of ocean
floor me lange. The fact that the ophi o l ite belt's
melange is ocean ic in origin is best displayed in
the record of oceanic sedimentation. As with the
ophiolite belt's igneous and metamorphic rocks,
petrogenesis of its sedimentary roc ks was sy ntectonic . Thus the ea rliest formed sedimentary rocks
are thoroughly mixed into serpentinite melange, with
later deposits being mixed to a lesser extent. In
the following discussion the oceanic sedimentation
history of the ophiol ite belt is treated in two sections, elastic and biogenic. It must be emphasized,
however, that these sedimentation modes operated
simultaneously.
Clastic Sedimentation
Sedimentary breccia and coarse angular sandstone composed of basalt, diabase, gabbro, and rare
chert and amphlbolite detritus occurs as me lange
blocks in severa l localities along the ophio lite
belt. Relict bedding is preserved in some blocks.
Sedimentary fabrics suggest both talus slope accumulation and debris flow deposition modes. In a
couple of blocks deformati on makes it impossible to
decipher If the breccia Is a deformed sedimentary
rock or If it originated in a fault zone. Angular
clast fault breccias along with rare sedimentary
breccias have also been observed in the pi I low s ection of the Bald Mountain slab . Since the se dimentary breccias occur most commonly as melange blocks
the deeper stratal levels of the ophiol ite were at
least locally exposed and eroded prior to melange
mixing. Deep level exposures of the ocean floor are
only known to occur along fault scarps of transverse
fracture zones (Bonatti and others, 1971; Mel son and
Thompson, 1971; Melson and others, 1972; Thompson
and Melson, 1972; Fox and others, 1976; Bonatti and
Honnorez, 1976). The mafic sedimentary breccias are
Interpreted as having been shed from fault scarps
formed during the early stages of ophlollte disruption . The breccias were subsequently engulfed Into
serpentlnlte melange as the fracture zone evolved
to a more chaotic state.
The brecciation sequence o utlined above is interpreted as having two intimately assoc iated stages.
The first stage is autobrecciation as the ultramafic
materia l moved up diapirically into the fracture
zone . The second stage i s dispersal of the brecciated
ultramafic rock as debris flows and turbidities upon
s urfacing of the ultramafic protrusion. In many
instances it is impossible to distinguish between
protrusive breccias and sedimentary breccias.
Brecc ias interpreted as definitely prot rusive are
part s of semi-intact peridotite b locks . Breccias
interpreted as definitely sedimentary contain sed imentary structures and clasts or interbeds of chert
(Fig. 4e). A s imil ar intimate relationship be tween
protrusion and sed imentary breccias can be observed
in ultramafic flows of the California Coast Ranges
(Eckel and Myers, 1946; Dickin son , 1966; Cowan and
Mansfield, 1970; Lockwood, 1972) , and are apparent
in modern fracture zones (Bonatti and others, 1974;
Bonatti and Honnorez, 1976).
Vertical protrus ion of ultramafic rock is known
to be an important process along modern fractur e
zone's (Melson and others, 1967, 1972; Thompson and
Mel son , 1972; Bonatti and Honnorez, 1976; Fox and
others, 1976) . The steep l y plunging e longation lineation (Li) within SJ indicates a dominant component of
upper mantle - lower crus tal vertical flow during and
immediate ly following ophlo l ite genesis (Fig. 4f).
In a fracture zone environment the accent of the hot
ultramafic rock would not be confined by lateral
spreading about the ridge axis. Thus S1-L1 development not on ly reflects wrench tectonics, but also
vertical protrusion tectonics . Protrusion was probably accelerated as water migrated Into the deforming
ocean floor and serpenti nization of the hot ultramaf ic rock commenced. The blocky fracture pattern
discussed above suggests a volume Increase during
serpentlnlzatlon. Similar patterns are present
150
NORTH AMERICAN OPHIOLITES
around the Burro Mountain ultramafic body of the
California Coast Ranges where expansion has been
documented (Co l eman and Keith, 1971). In addition ,
se rpentinite under high temperature conditions
ex i s ts in a therma ll y weakened state (Ralei gh and
Patters on, 1965) . Thus, the upward duet i 1e and ca tac 1as tic flow of peridotite is envisioned as having
accelerated due to the expansion and weakening of
serpentinization. As vertica l flow and serpentinizat i on progressed.the protrusive rock continued to
weaken. inc reasing its mob ility . The importance of
strain history wit h respect to progressive weakening
in these type of bodies has been demonstrated by
Cowan and Mansfield (1970) . Surfacing of the frac ture zone protrusions resulted in mono l ithologlc
sed imentary breccias of ultramafic rock.
Talus pi Jes of protruded ultramafic rock are
believed to be the main environment of ophicalcite
formation. Interaction with percolating ocean water
and/or hydrothermal fluids is believed to have been
the main cause of oph i calcite formation. A biogenic
origin is not considered important here since biogenic I imestones are rare along the entire ophiol ite
belt. A subaeria l pedogenic origin (Fo l k and
McBride, 1976) is not considered since radiolarion
chert i s loca ll y interbedded with and over li es
ophica l c ite.
The detrital ultramafic rocks show a comp lex
sedimentation history with abundant reworking .
Cl asts of ophicalcite containing abundant ultramafic
detritus occur in later generation ophica l cites and
in detr ita l serpentinites. In addition, interbeds
of ophica l cite occur within detrital serpent init e
and interbeds of both ophica lcite and det rital se rpentinite occur within radi o larian che r t . The ophicalcite interbeds appear to have been accumulations
of carbonate mud with pebble to sand size ultramafic fragments. In severa l ins tances these "diamicti tes" compose the matrix of chert-clast breccia.
As wil 1 be discussed in the section on biogenlc sedimentation, soft sediment deformation and reworking
was an i mportant process along the fracture zone .
The prot ruded accumulations of ultramafic detritus
and related ophica l cites were probably disrupted and
reworked by further protrusion and wrench tectonics .
Loca l disruption may have also occurred when sma ll
mounds of pillow lava were built on the detrital
ultramafic rocks.
The detrital ultramafic rocks were readily
incorporated into serpent inite me lange as both blocks
and matrix. In numerous instances the friable detrital s erpentinites can be observed in intermediate to
advanced s tages of di s integration into melange matr ix
by development of 52. The fact that the ultramafic
e la s ti c sedimentary rocks occur as depositional
remnants above me lange , as melange blocks and as a
local protollth of the melange matrix indicates
their syntectonic genesis.
Biogenlc Sedimentation
Deposition, sof t sediment deformation, llthificatlon and hard rock deformation of radiolarian
chert proceeded throughout the disruption plstory of
the ophlollte belt . The earliest formed cherts are
mixed as tectonic blocks throughout se rpentlnlte
melange, and occur loca l ly within pillow lava slabs
and melange blocks . Later-s tage cherts rest as
highly deformed depositional remnants above detrital
ultramafic rocks, late-stage pillow lava mounds and
serpentinite melange. Chert melange blocks conmonly
have stratigraphic thicknesses of about 20 m. Thicknesses between 100 and 200 m occur in the depos i tional remnants, but these are gross thicknesses due
to i ntense deformation. Since chert deposition was
syntectonic a coherent chert section probably never
existed. The thicknes ses of both the melange blocks
and depositional remna nt s suggest that at least 200
m of chert was deposited on the oph iolite belt prior
to deposition of the continental margin assemblage.
However, the earl i er- formed chert intervals were
tectonically mixed into melange prior to and du ring
deposi tion of the lat e r- formed intervals. Contact
metamorphic recrys ta lliz ation of radiolaria tests
prohibits pa leontol og i ca l dating of the cherts.
A sig nifi cant relation s hip ex i sts between the
composition of the cherts and the ir structural setting . Cherts occurring as tectonic blocks throughout the mel ange commonly contain black to dark purple
interbeds and disseminati ons of oxide minerals.
These impurities are pri mar i ly iron oxide with trace
manganese ox ide. The meta lliferous cherts are notably lacking in argillaceous or vo l canic impu ri ties.
Cherts occuring as highly deformed depos itional remnants above serpentinite melange locally contain
thin interbeds and disseminations of arg illaceous
materia l. The argillaceous cherts lack significant
amounts of oxide mineral s , and lack volcanic impurities. Vo lcan ic impur it ies occu r only rarel y in
cherts that occur with pil l ow lava. Cherts l acking
any significant impurities occur both as dispersed
melange blocks, with or without me talliferous
chert, and as bedded intervals in depositional remnants which contain the argillaceous cherts.
The relationships presented above are interpreted to be a result o f: I) deposition of radiolarian
ooze commencing during ophiolite genesis and continuing throughout ophiolite disruption along the fracture zone; 2) ear ly to midd le-stage deposition of
basal metalliferous sediments from hydrothermal so lutions (Bostrom and Peterson, 1969; Bostrom and
others, 1976) emanating from depth at the spreading
axis and possibly along the fracture zone for some
distance off the spreading axis; 3) la ter- stage
sporadic influx of fine terrigenous material shed
from a distant source that was be ing approached by
sea floor spreading transport of the f racture zone
complex. Following deposition of the argil laceous
cherts the next rocks that appear in the sedimentary record are chert-argi 11 ite olistostromes which
contain shallow water limestone o li sto l i ths, and
interbeds of both cont i nent derived sandstone and
argillaceous chert. Thus the ophiolite was approaching a landmass that was not contribut ing volcanic
detritus to the sedimenta ry record . Th is important
relationship will be discussed further in conjunction with continental margin tectonics.
Stratigraphic settings of the various cherts
indicate progressive disruption of the oceanic basement during blogenic sed i me ntation. The early to
middle-stage cherts occur In association with pillow
lavas or as dispersed blocks In serpentinite·melange .
These cherts appear to have had two depositional
settings: 1) mafic oceanic basement as shown by
their presence In both pillow lava s l abs and in pillow lava-bearing melange units; and 2) protruded
ultramafic basement as shown by their presence in
perldotlte melange units where they are associated
with ophlcalcite and detrital serpentinite . The
later-stage cherts were deposited on basement cons isting of serpentlnite melange. detrital ultramaflc
rocks and mounds of late-stage pillow lava.
KINGS-KAWEAH OPH IOLITE BELT - SALEEBY
Structura l features o f the c he rt assemb l age
reflect conti nuous deformational act i vity along the
fractu re zone. Str uct ures that are best interpreted
as soft sediment i n origin occur both in tecton i c
bl ocks and in the depos i tiona l remnants. These cons i s t of stratigraphic interva l s of chert-cemented
chert -c l ast brecc ias and associated chaotic fo l ds
(Fig. 4h) . The chaot i c in terval s are bounded by
bedded interval s both of which are common l y cut by
hard rock tectonic struct ures. In seve r a l instance s
chert c last deb ri s flow deposits occur with an oph i ca l c ite mat ri x. The common occurence of soft sedi ment brecc i as and fo ld s i s taken as an indicator of
an unstabl e depositiona l env ironment . Sin ce the
younger che rts over li e serpent inite me l ange , wh i ch
contains b l ock~ of o lder cher t s, the in stab ility of
t he pelagi c depositional env ironment is shown t o
have been persistent and tecton ic in orig in.
Earl y to midd le-stage cherts, whic h occur p ri mari l y as melange blocks, we re lithified in most
cases prior to me l ange mixing. This i s shown by the
presence of britt l e shear and tension fractures which
are the su r faces a long wh ich the me lange b locks initia ll y broke apart. Ducti l e deformation features
such as pinching and swe lli ng or streaking- out of
bedd ing in ma ny cases cannot be distingui s hed from
soft sedi ment features. In some instances chert
bl ocks can be shown to have been ducti l y defo rmed
a l ong wit h s2 deformation o f the matrix. Thus ea rly
to midd l e stage cherts underwe nt loca li zed chaotic
fo lding and brecc i at ion pr ior to l i t hif i cation, and
fol l owing l i thification t he y underwent brittle frag mentat ion to form me l ange b locks some of which underwent subsequent ducti le deformation a long with the
melange matrix.
Late-stage cherts which occur as depositional
remnants above me l ange are in some ways st ructura ll y
mo r e comp l ex tha n the ear li er-stage cherts. Thi s
relations hip i s interpreted as a res ult of deposition
and l ithification of the ear li er cherts occ ur ing on
semi -in tact basement s l abs undergoing l ocalized deformation with depos ition of t he lat er cherts occuring on serpent inite me l ange basemen t undergoing penetrat ive deofrmatlon . Thus , once li t hifi ed the ear l ier cherts were ab l e to escape much of thP. deformation that the l ate r che rt s expe rienced in a soft
sed iment to sem i-1 ithi fied sta t e whil e s itti ng on
active me l ange . Chaot ic fo lds and breccias of probable soft sediment orig in are loca ll y i mporta nt in
t he late-stage c herts. Another important feature of
these cherts, which ap pea r s to have been inherited
from the soft sediment to sem i-lithif i ed sta t e, i s
the presence of l arge ma5sive doma i ns wi t h loca l
c las ts and rootless folds . The massive domains grade
into o r s harpl y abut against bedded domains. The
massive doma ins are interpreted as ponds o f reworked
radiolaria ooze which s lid across and rippe d up beds
of compacted ooze. In additi on some chert bed s are
graded with respect to radi o l aria test size which
s uggests reworki ng of radi o l aria ooze by turbidity
c urrent mechanisms . Both bedded and chao tic domai ns
o f the depos iti ona l remnant s are common ly c ut by a
s pa ced c l eavage whi ch loca ll y grades into a penetrative c leavage. Where bedding l s preserved the c l eavage is occas i onally axia l planar to s t eep-p lung i ng
fold s . In seve ral ins tances the c l eavage c uts acros s
l imbs of chaotic soft sed iment fo lds . The c leavage
i s cop l anar to s 2 of the underl ying melange matri x .
The o utc rop pattern o f the depos it ional remnants ls
highly sugges tive of a n info ld relations hip with the
underlying melange (P late V).
It must be emphasized that a di sti nct line
151
ca nnot be d raw n be t ween ear l y , mi ddle and latestage cherts . Early and l ate-stage cherts can be
distinguished by the st ructure- composition re la tions
outl i ned above. Mid d l e - stage cherts appear to represent a grad ition both in struct ure and composition
between ear l y and la te-stage che rt s. The fact that
sof t sedi ment and progressive hard rock deforma tion
occur throughout the che rt assemb l age coupled with
the composit ional var iation out ! ined above indicates
that the ocean f l oor was prog ress ively disrupted in
an ocean i c environment en-route to the continenta l
env ironment. A s urvey o f presen t day marine tectonic
e nvironmen t s re veal s t hat a l a rge fract u re zone wi ll
se rve as t he onl y su i table analogue .
Fra ctu re Zone Tectonics and t he St ructu re of Ocean ic
Crust
The syntecton i c history of i gneous , metamorphic
and sedimentary petrogenesis disp l ayed in the Kings Kaweah oph iolite be l t i s diagramatically s ummarized
using a fracture zone model in Figure 5. Mafic
magma and harzburgite res i due are shown ascending
beneath the rid ge axis in accord wi th sea f loor
spreading theory (Green and Ringwood, 1967; Kay and
o thers , 1970 ; Green, 1970, 1971; Dewey and Bi rd ,
1971) . The mode l shows anoma lous ocean i c crust
being created at the intersection of the spreading
center and the ax i s of the fractu re zone . The anoma lous crust is shown as having two ma in components.
1) Ma fic pi ll ow lava, hypabyssa l and deeper p lu toni c
rock charac t er i zed by chaotic prot oclas ti c deformation a nd mixing . These rocks now exist as complex
me l ange b locks and me l ange units. 2) Ultrama f i c
protrus ions wh i ch ascended into the fra cture zone
from the ma ntl e while hot, and which upon reachi ng
crustal l evels underwent se rpentin i zat ion and s ubsequently surfaced,shedding ul tramaf i c detritus .
The large proportion of ultramaf ic rock along the
ophio l ite be l t, the common occurence of peridotitechert me l ange units, and the mono l ithol ogic nature
of most detrital ultramafic rocks indicate that a
s ignificant amount of anomalous oceani c crust was
crea ted by ultramafic protrus i on. I t fo ll ows that
a s i gnif icant amoun t of sp read ing probably occurred
along the ax i s of t he fra c ture zone due to protrusion tec tonic s. Thi s has been suggested for l arge
modern f racture zones (Van Andel and others, 1969;
Thompson and Me l son , 1972; Bonatti a nd Honnorez,
1976). In addition, p ro t r us ion t ect onics probab ly
p layed a s ignificant ro l e i n s e rp entin i te me lange
formation . The anomalous oceanic crust was generated in a semi-tectonically mixed state wi th chaoti cal l y deformed mafic c rusta l blocks interwoven wi th
ultramafic p rotrus ions and their sedime ntary derivatives. This configuration was subjected to prolonged
wrench tectonics which resu l ted in serpentinite
mela nge. The oceanic sedimentation record above the
se r pentinite melange indi cates that the me lange too
represen t s anomalous ocean i c crust . It i s suggested that se rpentinite me l ange i s a sign ificant anoma lous c r usta l component in present -day fracture
zones with l a rge ridge offsets.
The mode l a l so s hows a more convent iona l-ty pe
of ocean i c cr ust exposed by fau l ting along the margin of the fract ure zone. Thi s is presen tly represented by the Kings River oph io li te which has the
remnant s of normal ocean floor stra tig raphy (Fig. 2).
The relationship portrayed above i s best d isp layed
today a long the Verna Fracture Zone of the equatoria l
Atlantic whe re norma l ocean i c crust is apparently
exposed along the f racture zone's northern wall while
disrupted and protruded crust is exposed along its
a xes and southern wa ll (Bona tt i and Honnnorez , 1976) .
152
NORTH AMERICAN OPHIOLITE S
The e ffec ts of fracture zone tecto nics (pro trusive
and wrench) are ev iden t in the Kings Ri ve r oph io1 ite ; however, it s st rata l s uccession indicates t hat
norma l ridge cr us tal genera ti on processes were permitted to operate . Thi s pa tte rn is intui t ive l y
pleas i ng si nce anoma lous fracture zone c rust must a t
some interva l g ra de l ateral l y in to normal ridge
crea ted c rust . The Kings Rive r ophiol ite i s in terpreted as having o rigi nate d in s uch a g radat ion
in te rva l .
The comp l ex i ty of t he ophiolite belt s S1 tect on ites can be conceive d o f as a resu l t of both
wren ch and protrus ion tecton i cs. As t he hot uppe r
mant le and lowe r c r ust ascended i nto the fracture
zon e i t was po l ydeformed. The de formation s cons i s t
of: 1) vert i cal ext ens i on by upwa rd flow; 2) f lattening in the p l ane of the fra c ture zone by forcing
it s c rusta l l eve l s apa rt during pro trus ion ; 3) s hear
and trans la t ion in the pl ane of the fracture zone
by wrenc h fau l t ing; 4) ro tation and foldin g abo ut
steep axes in the plane o f t he fra c ture zone due to
wrench movements ; and 5) a probab l e complex system
of di p- s lip fault s , antithetic str i ke- s lip fa ults
and shal low plungi ng fo lds that are ub iquito us in
continental wrench zones (Moody a nd Hi 11 , 1956;
Lil 1 ie, 1964; Reed, 1964; Di ck inson, 1966 ; Harding,
1973, 1974 ; Wil cox and othe rs , 1973; Sy l ves t e r and
Sml th, 1976).
The fact th a t fracture zone deformat ion of the
ophi o lite belt wa s progress i ve i s well-disp l ayed by
the contrad i c t ory cross- cu tti ng relation s between
steep to s hal low plung ing folds, different st age s 1
s urfaces, and different stage i gneous pu l ses. The
in c lus i on of che rt blocks in se rpe ntinite me l ange
and the depos iti on of l ater-s tage che r ts ac ross the
melange with the ir subseq uent defo rmati on demons trates the longev ity of progress i ve deformation .
As o utli ned in the next section, th i s defo rmation
conti nuum i s be l i eved to ha ve extended from the
ocea n ic real m into the a nci ent continenta l marg in a s
the ophiol i te belt wa s transported a nd emp l aced into
its present pos i t i on.
GREENXHISTAMPHIBOLITE c'0~EISOGRAD f~p.
RIDGE
MAGMATISM
Figu re 5. Schematic block diagram showi ng how cr itical features o f the Kings - Kaweah oph iolite belt fit
into an oceanic fract ure zone tectonic model. Regional relationships suggest a north-south trend for the
fracture zone making this view of the block diagram
towards the northwest.
THE ANC IENT CONTINENTAL MARGIN
The fract ure zone mode l for the o r igin , deformation and sea -fl oo r sp r ead ing trans po rt of the
Kings - Kaweah op hi o li te be lt has been de ve loped above
us ing data so l e ly from the oph iolite be l t it se lf.
The fracture zone hi sto ry of the ophio l ite be l t
appa re ntly began in the l ate s t Pa leozo i c and probab l y extende d into the Tri ass ic. Recent wo rke r s
have c ite d reg i ona l st r uctu ral and stratig r ap hic
ev idence for ea rl y Mesozo i c tectonic truncati on and
tra nscur rent fau l ting o f the ancient southwest con tinental margin (Hamilton a nd Myers , 1966; J ones
and o the r s , 1972; Jones and Moore , 1973; Burchfi e l
and Da vi s, 1972; Silve r and Ande r son, 19 74;
Schweickert, 1976) . Thi s tectoni c regi me is be li eved
t o have been direct l y re lated to fracture zone tect on ics as discusse d above. Thus the f ra cture zone
i s believed to have extended from wel l within the
oceani c rea lm into the anc i ent continenta l margin .
Outstand ing modern examp l es of complex wrench s ystems
which in vo l ve both ocean i c and continenta l domains
inc lude t he Macquar i e Ridge-Alpine Fault sys tem of
the southwest Pacific (Griffiths, 1971; Griffith s
and Varne , 1972), the San Andreas - Queen Char lotte
sys tem which rims western No rth America (Wi l son,
1965) and the Spit s bergen Fracture zone of the
Arct i c Ocean (Lowe l l, 1972). Consider i ng the complex
histories of these sy tems one is forced to conc lude
that s ignif i cant comp l ex ities that cou ld have invo l ved trip le junctions and mi c ropl a tes are probably
irreso l vab l e i n the ancient s ys tem. Wit h thi s in
mind, a s impli s ti c tecton i c mode l i s out lined below
for the continen t a l margi n deformat ion and emplacement of the Ki ngs-Kaweah oph iol ite be l t. A fu ll er
treatment of thi s model i s give n in Sal eeby and
others (in prep.) and Sa l ee by (in prep. b) .
Foothi 11 Suture
The Sier ra Nevada foo thi ll metamo rphic be lt
co in cides with a tectoni c s uture i n the earth's
c rust (Fig. 1) . Suture i s used he re to mea n a zone
of joining. As discus s ed be low the foothi 11 s uture
joins foss il l ate Pa l eozoic t o early Me sozo i c ocean ic
1 i thosphere to o lde r continental 1 i thosphere. In the
south the sut ure i s defined by the Ki ngs - Kaweah
ophi o li te be l t. In the north it i s defined by the
foo thi 11 fault system (C l ar k, 1960; Schwe i cke r t and
others, 1977). The significance of the foothi ll
s utu re i s s hown by se veral po in t s : 1) all Sierra
Nevada oph i o li te remnants occur a long it ; 2) hi ghly
deformed a nd tecton i cally mi xed rock s whi ch occur
a l ong it (C lark, 1960, 1964; Morgan, 1973 ; Duffi e ld
and Sharp, 1975; Eh renberg, 1975; Behrman , 1978;
Sa leeby , i n press a , b) indicate that it was a zone
of major trans la tion; 3) t he di s tinc t changes in the
g ross s truct ure of the c rus t and upper mantle which
coincide with the s uture (Fig . 1, in set) can be best
explained as a res ult of a fossi l contact between
oceanic and continental l ithosphere; 4) Jurass i c and
Cretaceous ba tholithic rocks emp l aced into an d to the
east of the suture have sys tematic petrochemica l
varia ti ons (Fig . 1, in set) which can be best exp l a ined
as a res ult of t he batholith hav ing been empl aced
across a contact between ocean ic and contine ntal l lth~sp here; and 5) as discuss ed below highly contra s ting
li tho logic and s tructural terranes are juxtaposed
a l ong I t (Fig . 1).
The s uture in the south i s exposed as a penetratively deformed ophiollte terrane, whereas in the
north it' s exposed as a fa ult system in primari ly
younger epic la stic and arc volcanic rocks . This i s
believed to be a result of deeper level s of exposure
KINGS-KAWEAH OPHIOLITE BELT - SALEEBY
occ urr ing towards the sout hern end of the metamorphic
belt as di sc ussed ear li er. Many of the penetrative
de format ional features present in the metamorphic
belts ophi o litic basement rocks pre-date overlap by
the younger epiclastic and arc volcanic rocks. Defo rmational features in the younger rocks and the
foothi ll fault system are the last expressions of
deformation along the suture. It is s ignificant
that these late-stage deformations fo llowed the
o lder trends estab li s hed in the ophio litic basement
rocks.
The foothill suture represents the locus of sig nificant tectonic juxtapositioning. Late Paleozo ic
oph iolite remnants and over l ying ea rly Mesozo ic epiclastic and arc volcanic rocks are juxtaposed against
a complex of Paleozoic to early Mesozo ic continental
marg in rocks which lie east of the suture. These
rocks appear to be remnants of the fragmented continental margin. This f ragmentati on is be lieved to be
linked to fracture zone tectonics of the Kings-Kaweah
ophiol i te belt, and to emplacement of the ophiol ite
belt against the continent's edge.
Continental Margin Fragmentation
Paleozoic rocks east of the Sierra Nevada const itute the so uthe rn end of a system of paleogeographic belts that can be traced as far north as
central Alaska (Churkin, 1974) . The paleogeographi c
belts consist of volcanic arc, marginal basin and
shelf terranes (Fig. 1). Through eastern California
and Nevada the paleogeographic belts have northeast
trends which are exemplified by facies patterns and
Paleozoic thrust belts (Fig. I) . The s helf rocks
appear to overlie pre-Phanerozoic crystalline basement, whereas marginal basin and volcanic arc rocks
were apparently deposited on transitional or oceanic
basement.
Remnants of the Paleozoic belts are present in
roof pendants of the eastern Sierra Nevada and possibly in the Shoo Fly complex of the northern Sierra
Nevada (Speed and Kistler, 1977; J.N. Moore, persona) convnunication, 1977). These exposures mark the
western 1 imit of the Paleozoic belts, and thus a
zone of pre-batholith tectonic truncation must have
passed longitudinally through the Sierra Nevada .
Tectonic truncation of the Paleozoic belts is
be lieved to have been a direct result of wrench
movements along the foothill suture. The foothill
suture is envisaged as a segment of a transform
plate juncture which extended from the fracture zone
and cut obliquely across the ancient continental
margin. Fragments of the Paleozoic belts were displaced by oceanic lithosphere during truncation.
Truncation of the Paleozoic belts resulted in
a major change in the s tructural grain of the southwest continental margin. Northeast structural and
stratigraphic trends, which prevailed throughout the
Paleozoic, were terminated and replaced by Mesozoic
northwest trends (Fig. I). The northwest trends
have persisted through the Cenozoic and are now
manifested by the San Andreas fault system.
This change in structural grain is evident
within Paleozoic strata adjacent to the truncation
zone. In Paleozoic strata exposed immediately east
of the Sierra Nevada northwest trending fold axes,
cleavages, thrust faults and strike-slip faults of
Mesozoic age are superposed over earlier northeast
trending structures (Stewart and others, 1966 ;
Burchfiel and others, 1970; Stevens and Olson,
153
1972; Kelley and Stevens, 1975; Sy l vester and Babcock, 1975 ; Dunne and Gulliver, 1976; J.N. Moore,
personal communication, 1977; Saleeby, unpub. data).
A simi lar patte rn of superposed structures exists
in Paleozoic rocks present in roof pendants of the
eastern Sierra Nevada (Kistler, 1966; Brook, 1977;
Rus sel and Nokelberg, 1977). It must be emphasized
that the northwest trending structu res of the Sierra
Nevada do not represent a sing le deformational event.
In stead, deformation along northwest trends occurred
continuously, o r in numerous pulses, throughout the
Mesozoic (Nokelberg and Kistler, 1977 ; Saleeby, i n
prep . b).
Roof pendants east of the Kings-Kaweah ophiolite
belt record the history of early Mesozoic sedimentation and tectonics along the fragmented edge. These
rocks a re treated in-depth in Saleeby and othe r s (in
prep.). As discussed ea rli er they cons i st of continent derived massive sa ndstone, flysch, olistostromes
and an upper sect ion of s hall ow marine and si l ici c
volcanic rocks. Thi s assemblage was probably depos ited on continental crust as shown by i sotop ic
studi es on their enclosing bathol ithic rocks (Kistler
and Peterman, 1973, 1975 ; Doe and Delevaux, 1973;
Chen, 1977). However, this assemblage may not be
in it s or i g inal position relative to s i mil ar age
rocks resting above Paleozoic st rata immediately
east of the Sierra Nevada (Jones and Moore, 1973;
Sa l eeby and others, in prep).
The e lastic rocks
we re reworked from the truncated Paleozoic she l f
be lt. They we re apparently shed as s ubmarine aprons
and fans across fragmented continental basement.
The basement was probably undergoing l ong i tudina l
wrench movements along the new Mesozoic trends
during elastic sedimentation. This tectonically
active depositional environment i s believed to have
g iven ri se to the chaotic deposits of this assemblage.
Structural data on Paleozoic and Mesozoic continental margin rocks east of the Kings-Kaweah ophio1 ite belt suggest that a longitudin a l dextral wrench
system worked in conjunction with transverse shortening during the early Mesozoic (Saleeby, in prep.
b). This pa tte rn is also evident along the KingsKaweah ophiolite belt. These structural patterns
suggest that the fracture zone complex was transported from the south, and that the continenta l
margin f ragments were displaced northward .
Plate tectonic transport of the ophiolite belt
and the displaced continen tal fragments to the
north i s also impli ed by regional considerations.
1) Lowe r Paleozoic rocks of southeastern Alaska
constitute part of an anomalous continental fragment which may have been transported by right-slip
faulting from the California region (Mongar and
Ross, 1971; Jones and othe rs, 1972). 2) Another
anomalous terrane of Triassic age, which extends
from south-central Alaska through British Columbia ,
has yielded equatorial pa leolatitudes (Jones and
others, in press). 3) Plate tectonic reconstructions of the Mesozoic western Pacific y i el d mainly
east-west trending spreading axes with large northsouth trending fracture zones (Larson and Chase,
1972; Hilde and others, 1977) . In addition, there
is known to have been 4,500 km of northward drift
of the Pacific ocean floor since the middle Mesozoic
(Larson and Chase, 1972). The time intervals for
which these plate tectonic relations are applicable
post-date the fracture zone history of the ophlo1 ite belt. However, the consistency between these
relations, and the structural configuration of the
154
NORTH AMERICAN OPHIOLITES
oph iol i te belt an d t he ancient con ti nen tal ma rgi n
s uggest tha t al I of these tectonic process es a re
related to th e same kinema ti c reg ime .
Continental ma rgi n rocks l y i ng above the oph io1 it e belt record i ts t ranspo r t histor y in to prox imity
of Nort h America. The chert-argillite o li stost rome
comp l ex was acq uired at some unknown di stance from
the contine nta l margin duri ng t ransport f rom the
South Pac i f ie (Sa lee by a nd others, in pre p.) . Large
s ubmari ne slid ing cove ring thous ands of sq uare kilome t e rs of ocean f loor i s a s ign ificant modern process
adjacent to both s ta bl e and mobi l e cont inenta l margin s (T . C. Moore and o thers, 1970; Embley, 1976;
D.G. Moo re and ot he r s , 1976). The source fo r th e
an c ie nt o li stost rome comp l ex is unknown. The exo tic
nature of the fau na with in I imes tone o l i s t o l ith s
indicates that t he source was not the North Amer i ca n
continent. The o l i s tos trome comp l ex and it s exot i c
fa una may have been derived f rom ou tboard borde rland
and/o r o rogen i c terranes wh i ch r immed the weste rn and
southern ma rg i ns of North America in t he l atest Pa l eozoic (Sa l eeby and ot hers , in p rep. ).
I t is s ign i ficant that the che rt -a rg i I li te
o l i s to s trome comp l ex grades into di s tal quartoze to
subarkos i c f lysc h. Furthe rmo re , thi s f l ysc h sequence
appears to be the d i sta l equival ent of e last i c rocks
shed direc tly of f the fragme nted North Amer i ca n Paleozoic shelf. The ex trem iti es of a large s ubmarine
fan syst em de ri ve d from the fragmented s helf are
envisaged a s lapping acros s the cite of f ina l cher targil li te deposition. The poss ibl e spatia l an d temporal comp l ex iti es of this re l at i onship are di sc ussed
in Sa l eeby and othe r s (i n prep.).
Sho rtl y after e la st ic sedi menta ti on began s ubduction tectonics commenced a long the Mesozo ic
trend s. Thi s is s hown by the remnant s of the arc
rocks a l ong the oph i o l ite be l t and th e ea rly Mesozo i c s ili c i c volcanic rocks eas t of the ophi o l ite
belt. Regional age data on vo l canic and p lutonic
rocks s uggest that th i s trans iti on occurre d during
the Tri assic (Evernden and Ki s t l er, 1970; Crowder
and others, 1973; Schwe icke rt, 1976b ; Morgan and
Stern, 1977; Sa leeby and other s , in prep.; P.C.
Bateman and O.T. Tobi sch, ora l communication, 1977).
Subduction a nd Ophiol ite Emplacement
Tran scu rrent (wrench ) faulting ha s recently been
cited as an impor tant mechani sm for ophiol i te
emplacement alo ng continental margins (Dewey and
Karson, 1976; Brookf ield, 1977). In this view in i tial juxtaposition of ocean ic lithosphere against
cont inenta l 1 ithosphere occurs by wrench faulting,
and actua l oph io l ite emp l acement occurs during a
change i n plate motio ns which res ults in a convergent component between the juxtaposed plates. A
s imilar mechanism is env i saged for the Kings-Kaweah
ophiol ite be l t (Fig. 6) . I t is not unreasonable to
assume that the ancient fracture zone complex was
ten s of k il ometers wide during the l ater stages of
its evoluti on - considering the width of modern
fracture zones with l arge offsets (Thompson and
Me l son, 1972; Sc later and Fisher, 1974; Bonatti and
Honnorez, 1976). A widely accepted corol lary to
plate tectoni c theory is that continenta l lithosphere cannot be s ubducted beneath oceanic lithosphere due to their relative densities (McKenzie,
1969). Similar logic is used in deciphering the
fate of the fracture zone complex during the onset
of subduction. Taking into a ccount that much of the
fracture zone complex was serpentinite, and that
serpent1n1te i s s ignificantly l ess dense than
cont i nental crust , the cons uming brea k is believed
to have formed on the oceanic side of the fracture
zone comp lex . Thus the change in plate motions
accreted the fracture zone complex to the "raw edge"
of the continental margin. As the transform juncture evo lved into an oblique s ubducting j uncture the
fracture zone comp l ex was stra nded as the s ubduction
zone's hanging wa ll. Evo l ution of large fracture
zones into s ubduction zones during changes in plate
motions ha s been postulated for severa l present day
Pacific s ubduction zone s (Uyeda and Mi yashi ro, 1974 ;
Falvey, 1975; Hilde and o the rs , 1977) . At l east one
of these insta nces (Tonga-Kermedac) has yielded
ophi o l ite assemblage dredge hauls from its innertrench walls (Fisher and Enge l , 1969).
Fo ll owing the change in p l ate motions the accreted fracture zone complex served as fronta l arc basement. Howeve r, the arc rocks and their ophiol itic
basement are not considered to ha ve been in their
fina l position along the foothi 11 suture unt i I the
end of the Jurass i c when tectonic deformation along
the ophio li te be l t ceased.
As s tated earlier, the arc plutonic and volcanic
rocks o f the Kings-Kaweah region were syntectonica ll y
generated. Studies in the foothi 11 metamorphic belt
further north and in roof penda nt s to the east reveal
similar re l at ions (Parki son, 1976; Noke l be r g and
Kistler, 1977; Behrman, 1978; Saleeby, in prep . b;
Sa 1eeby and others, in prep.). In the Ki ngs-Kaweah
region the arc plutons were protoclastical ly deformed
whil e the volcanic seq uence was faulted and in some
instances penetratively deformed. There were a l so
uplift s and exposures of ophiol ite basement which
s hed ol i s tostromes into the arc seq uence. The structural trends of the arc deformation followed preexisting trends in the ophio li tic basement. I t must
be emphasized that Tria ss ic and Jurassic arc rocks
throughout California represent only small fragments
of the original arc terrane. The original position
of these fragments re lative to one another may not
be easily reso l ved.
Longitudinal wrench disruption and dispersion of
active arc and inner trench wall terranes i s known
to be an Import ant process along the modern circumPacific in zones of oblique convergence (Allen,
1962, 1965;. Allen and othe rs, 1970; Wilson, 1965;
Fitch, 1972; Karig, 1974 ; Karig and others, 1975,
1977 ; Brookfield, 1977 ; Curray and others, in press).
A signi f i cant northward component in Mesozoic
oblique subduction is believed to ha ve been dissipated by intra-arc wrench movements along the foothi 11 suture and within the fragmented edge of the
conti nent. Transverse shor tening worked in conjunct ion with longitudinal wrench movemen ts. This
transpressive (after Harland , 1971) tectonic regime
i s be li eved to have been facilitated by the preweakened state of t he arc basement which consisted
of the fragmented continental edge and the tectoni ca lly accreted fracture zone complex.
CONCLUSIONS
The Kings-Kaweah ophiolite belt was generated
during the latest Paleozoic at a distant east-west
trending oceanic spreading center where cut by a
major north-northwest trending transverse fracture
zone. The fracture zone extended from the oceanic
realm into the ancient southwest continental margin
where it truncated earlier northeast trending structures and facies patterns.
KINGS-KAWEAH OPHIOLITE BELT - SA LEEBY
155
WRFNCH DISRUPTION OF
WI-STERN NOR1/I AMCRICAN
PALEOZOIC OROGrN
Sii
tCJ('
- - I 01 CANIC
TGiR/\Nt
LOlvJl!vUFO
INFLUX or
QUART LOS(
U[ TRIWS
/
I
/
S OUTH
PA CI/IC
OCEA N
FLOOR
PERMO-TRIASSIC
TRIASSIC
JURASSIC
Figure 6. Series of block d iag rams which s how continenta l margin emp l acement h i story of Kings-Kaweah ophi o lite
belt. Vi ew i s northwa rd along the foo t h il I sut ure .
Along the axis of the fracture zone anoma lous
oceanic c rust was created. Thi s cons isted of protoclastically deformed maf ic igneous rock and protruded
ultramaflc rock . Away from the axial r eg ion of the
fracture zone normal oceanic crust was created. Remnants of the norma l crust also s how the effects o f
fracture zone deformation howeve r. Metamo rphictectonites of greenschist and amphibolite facies were
created dur ing fracture zone tectonics. The heat
which drove the metamorphic reactions was the amb ient
heat of ophlolite genesis . Protrusion and wrench
tecto nics worked together to progressively disrupt
the newly created ocean f l oor. Progressive di sruption and serpentinization led to the development of
serpentin ite-matr i x me l ange.
Oceanic sedi mentation proceeded throughout the
genesis and disruption history of the ophiol ite be l t.
Hafi c and ultramafic detrital rocks were shed off of
upfaulted and protrusive highs. Radiola ri an chert
was also deposited during genesis and disruption.
The earlier formed ocean ic sedimentary rocks were
thoroughl y mixed into serpentinite me lange. Later
deposits were mixed to a lesser extent. Several of
the latest deposits remain as high l y deformed depositional remnants above melange. The latest formed
cherts have local interbeds of argi 1l aceous material
which record encroachment of the fracture zone complex into the con tinent a l margin environment.
As the ophiolite be lt was transported no rthward
along the fracture zone into proximity of the conti nental margin fragments of the continental margin
were displaced by wrench movements . Chert-argillite
ollstostromes with blocks of sha ll ow water late
Permian limestone containing exotic fauna were shed
across the fracture zone complex enroute to the continental margin. By this time the ophlollte belt
had already been chaotically mixed by fracture zone
processes. As the ophi o l ite belt moved i nto c loser
proxim i ty of the truncated marg i n terrigenous sedi mentat i on overwhe l med hemi-pelagic sedimentation.
During the Tria ss i c a signif i cant convergent
component had developed along the fracture zone.
Disrupted ocean f l oor of the fractur e zone was
accre ted to the truncated edge of the cont i nent a s
the hang ing wal l of an obi ique s ubduction zone. A
magmatic arc deve loped a l ong the fragmented edge of
the cont inent in r esponse to subduction . The arc
l apped across th e suture between the accreted fracture zone complex and the truncated edge of the continent . As the arc evo l ved it was deformed and disrupted by both transverse s horten ing and continued
wrench movements. Arc deforma tion was faci l itated
by basement mob ili ty. The basement consi s ted of a
wide zone of fragmented ocean floor and continental
ma rg i n rocks .
The t ec tonic regime out lined above led direct ly
to the Franciscan regime and the related emp l acement
of the major part of the Si erra Nevada batholith.
The Cretaceous batho li th f urther disrupted and metamorphosed the Kings -Kaweah oph iol ite be l t l eaving it
as a healed tectonic s uture in the earth's crust.
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